The overall objective of this research grant is to characterize the pattern of prolactin secretion during the reproductive states of the rat and, when established, to investigate the ovarian and hypothalamic factors regulating these patterns. Also, to determine the role played by the secreted prolactin in regulating corpus luteum and mammary gland function. Cervical stimulation in the rat institutes two daily surges of prolactin secretion, one diurnal and one nocturnal, which continue for the greater part of the 12 day pseudopregnancy. Removal of the ovaries soon after cervical stimulation reduces by half the period of time over which these prolactin surges are secreted, suggesting that cervical stimulation only initiates secretion of the surges which are subsequently prolonged by ovarian steroids. This conclusion was confirmed by demonstrating that cervical stimulation of long-term ovariectomized rats resulted in an abbreviated pattern of secretion as compared with intact animals. In these same ovariectomized animals, it was found that the time of day at which the surges were secreted was constant and not related to the time of day at which cervical stimulation was applied. These studies in the rat have provided significant guideposts for similar studies in humans and will continue to in the future.